Hydraulic actuators are utilized in various industrial and other applications to provide movement in opposite directions under the control of hydraulic fluid supplied by a control valve unit. For example, material handling systems, conveyors, indexers, metal removal machines, cold forming machines, feeders, automatic loaders, and door control positioners, etc. utilize hydraulic actuators to control positioning of components during operation. Certain hydraulic actuators are of the rotary type and thus provide rotary movement and positioning, while other hydraulic actuators are of the linear type such as hydraulic cylinders for providing linear movement and positioning.
The U.S. patent of Barlow No. 3,954,045 discloses a control unit for a hydraulic actuator wherein a valve that supplies hydraulic fluid to the actuator is controlled by a solenoid assembly and a cam mechanism in order to control movement of the actuator. Cams of the cam mechanism are contoured to control the opening of the supply valve in cooperation with the solenoid assembly in order to control the actuator movement.
Other hydraulic control valves are disclosed by U.S. Pat. Nos. RE 29,329; 2,879,644; 3,640,069; 3,693,385; 3,779,136; and 3,780,623.